It is known that the dermis has a high density of capillary blood vessel when compared with an epidermis or a subcutis and also a lymph vessel end exists therein, so that in particular, a medical agent injected thereto directly is shifted to a blood vessel or a lymph vessel and an absorption speed thereof being absorbed in the body fluid is speedy. In particular, it is possible in the dermis to make a medical agent using a macromolecular substance such as hormone, antibody drug, cytokine and the like to be absorbed into the blood efficiently. Also, it is known that the dermis is a place of efficient immunity and it is possible to make a saving of applied dose of vaccine or to strengthen sensitization of a weak vaccine, so that it is possible to make a saving of immune cells to be administered or to strengthen the effect thereof.
Also, it is known for adult human beings that the dermis exists approximately in a certain amount of depth from the body surface (surface of stratum corneum). In other words, this fact means in case of injecting a medical agent into the dermis that it is possible to use a puncture needle having the same length (depth) with respect to these human beings.
Generally, the width of the dermis is around 1 mm to 4 mm (average value is 1 mm to 2 mm) if the vertical direction with respect to the body surface is made to be a reference and also, as shown in FIG. 29, the dermis exists in the skin so as to be sandwiched between an epidermis E which includes a stratum corneum and has width of around 0.06 mm to 0.1 mm and a subcutis S.
Accordingly, it is difficult to insert an tip portion of the puncture device, for example, a needlepoint of the puncture needle accurately to the dermis which exists between the epidermis and the subcutis, and if the needlepoint is inserted erroneously to the subcutis or the like, there occurs a problem such that a medical agent cannot be absorbed efficiently.
In recent years, for example, it is attempted that the macromolecular medicine mentioned above is administered continually or by one-shot into the dermis as a target, and in such a case, in particular, the above-mentioned problem becomes conspicuous.
Here, a hypodermic injection device is known in which the length of the puncture needle to be inserted into the body is defined in order to inject a medical agent to the dermis in the body (Patent Document 1). In addition, a medicinal solution injection device is also known in which the depth (insertion depth) of the puncture needle to be inserted into the skin is defined to be a predetermined length in order to inject a medical agent into a specific layer which exists in the skin and the puncture needle is inserted into the skin from the vertical direction with respect to the body surface (Patent Document 2). Also, a medicinal solution injection device is known in which a medical agent or the like is injectable with a predetermined pressure (Patent Document 3).
[Patent Document 1] Japanese Patent Laid-open No. 2001-137343
[Patent Document 2] Japanese Patent Laid-open No. 2005-87519
[Patent Document 3] US Patent Publication No. 2005/256499